The present invention relates to an electromagnetic clutch in which a shaft rotatable about an axis thereof is electrically connected to an input-side rotary member such as a gear, which is rotatably mounted onto the shaft.
Generally, an electromagnetic clutch of the above type is used as a part operatively connected to a sheet feed mechanism of an image forming apparatus such as a copier. As an example, the electromagnetic clutch includes a shaft rotatable about an axis thereof, an input-side rotary member (a gear), an output-side rotary member (rotor), a drive transmitting member (an armature) which is provided between the gear and the rotor and rotatable together with the gear. When the armature is magnetically attracted to the rotor against an urging force of a plate spring or the like due to a magnetic flux generated by an electromagnetic induction generating section, the rotation of the gear is transmitted to the shaft.
The electromagnetic clutch having the above construction is, for example, shown in the cross-sectional diagram of FIG. 18. In FIG. 18, numeral 51 is a rotor, 52 is a center through hole of the rotor 51, 53 is a shaft, 54 is a knurled threaded portion formed on the outer circumference of the shaft 53. The electromagnetic clutch is assembled in such a manner that the shaft 53 is pressfitted into the through hole 52 of the rotor 51 with the knurled threaded portion 54 of the shaft 53 pressing the rotor 51 at a portion corresponding to the through hole 52. Alternatively, the rotor 51 is loosely mounted onto the shaft 53 and then fastened thereon by swaging the rotor 51 at a part corresponding to the through hole 52.
In the above-constructed electromagnetic clutch, press-fitting or swaging is necessary when mounting the rotor 51 onto the shaft 53, which makes an assembling operation of the electromagnetic clutch complex.
Also, when mounting the rotor 51 onto the shaft 53, an unnecessary external force may be exerted on the rotor 51, and an undesirable mechanical stress may be generated on a surface of the rotor 51 toward which an armature is electromagnetically attracted. As a result, a magnetic attraction force on the surface of the rotor 51 may vary. In view of the above drawback, it is necessary to mount the rotor 51 onto the shaft 53 with an utmost care, which may further make the assembling operation cumbersome.